1. Field of the Invention
The invention relates to the driving of a light-emitting diode (LED); in particular, to an AC-to-DC LED driving apparatus for illumination and operating method thereof.
2. Description of the Prior Art
Recently, LED has been widely used in many applications. In a conventional linear LED driving circuit, no matter single segment driving or multiple segments driving is used, when the input voltage is smaller than a forward voltage of the LED, the current passing through the LED will be zero. In order to reach average current having best illumination efficiency, the LED current should be increased and the power and temperature will be also increased.
If a LED string has a first light-emitting diode, a second light-emitting diode, and a third light-emitting diode coupled in series, as shown in FIG. 1, in the periods of ΔT1, ΔT2, and ΔT3, a first LED current ILED1, a second LED current ILED2, and a third LED current ILED3 are zero respectively. Because the first LED current ILED1, the second LED current ILED2, and the third LED current ILED3 are all zero in the period of ΔT1, it means that the first light-emitting diode LED1, the second light-emitting diode LED2, and the third light-emitting diode LED3 fail to illuminate in the period of ΔT1, so that the LED string will generate flicker of 120 Hz.
Therefore, the invention provides a LED driving apparatus and operating method thereof to solve the above-mentioned problems occurred in the prior arts.